Fast-sync will not make you go any faster FPS wise, but it will allow you to go faster FPS wise, and notice the difference in the wording.

What I am saying is that V-sync ON will only allow you (in your and my case) to max out at 144 FPS. With Fast-sync, this barrier is removed and you can get higher than 144 FPS in the game. If you have ever tried V-sync OFF, you will notice that your game will run as fast as your GPU can pump out FPS, but at the price of constant screen tearing. With Fast-sync, your GPU will again pump out the FPS as fast as it can, but WITHOUT the screen tearing now.

Your Fast-sync kicks in only above what ever you set your monitor Hz at, i.e. if you monitor is set at 60 Hz, Fast-sync kicks in at 61 FPS, if you set your Hz at 144 Hz, then Fast-sync kicks in at 145 FPS.

Fast-sync has absolutely nothing to do with time compression, that is all CPU calculations, not GPU rendering.